As is well known, chlorine dioxide gas is a strong oxidant, and because its oxidizing action is effective in sterilization and decomposition of malodorous substances, chlorine dioxide gas has been used in disinfectant, deodorant and the like. The chlorine dioxide gas is dissolved in water in 20 times its volume of water, to give a brown aqueous solution. From the viewpoint of easiness in handling, it is desirable to use chlorine dioxide in a form of such an aqueous solution.
When the aqueous solution of chlorine dioxide is brought into contact with air, chlorine dioxide gas is rapidly generated. Therefore, there has been proposed a technique in which chlorine dioxide gas is constantly generated while maintaining its stability, by dissolving chlorine dioxide gas in an aqueous solution of sodium peroxycarbonate, and thus by forming an aqueous solution containing sodium chlorite as a main component with retained alkalinity (pH 9), i.e., what is called a stabilized aqueous solution of chlorine dioxide (see Patent Document 1).
However, when the alkalinity is retained in the stabilized aqueous solution of chlorine dioxide, a generation amount of free chlorine dioxide gas having disinfecting and deodorizing effects or the like is extremely low, and thus the solution has a low pharmacological activity. Accordingly, it is difficult to attain satisfactory disinfecting and deodorizing effects or the like.
Therefore, in order to enhance the pharmacological activity of the stabilized aqueous solution of chlorine dioxide, an acid has been added immediately before its use to lower the pH to 7 or less, for generating chlorine dioxide gas.
However, with this technique in which an acid is added immediately before its use, there arise economical problems that processes and equipments or facilities to implement the processes are required in order to enhance the pharmacological activity of the stabilized aqueous solution of chlorine dioxide. In addition, since chlorine dioxide gas is rapidly generated as a result of the addition of acid, it is difficult to expect a sustained pharmacological activity of the stabilized aqueous solution of chlorine dioxide. Moreover, a pharmacological activity is not retained constant and sometimes reaches an extremely high level, which raises safety concern about effects on animals, especially on human being.
In order to solve the above-mentioned problems, there has been proposed a technique in which a mixture prepared by adding an organic acid, such as citric acid, to chlorite is blended with a dissolved chlorine dioxide solution, to thereby maintain a chlorine dioxide concentration nearly constant for a long term (see Patent Document 2). In this technique, carbon dioxide gas is not rapidly generated, and a desired pharmacological activity is sustained by maintaining the chlorine dioxide concentration constant for a long term. In addition, even when dissolved chlorine dioxide is continuously released by portions as chlorine dioxide gas, the chlorine dioxide concentration can be held in an approximately constant range.    Patent Document 1: Japanese Patent Application JP61-181532A    Patent Document 2: Japanese Patent JP3110724B